Russia's ambassador to Turkey was shot dead in front of a crowd at a posh art gallery in the capital Ankara as the angry gunman screamed: "Don't forget Aleppo".
Police later killed the assailant on Monday night, Turkish station NTV reported.
Andrey Karlov, 62, was several minutes into a speech at an embassy-sponsored photo exhibition when a man who stood directly behind him in a dark suit shot the diplomat in the back from close range multiple times.
Russia's foreign ministry spokeswoman Maria Zakharova made the announcement of Karlov's death in a live televised statement.
Burhan Ozbilici captures Andrey Karlov's final moments
The assailant was a 22-year-old off-duty police officer who worked in Turkey's capital, said Ankara's mayor, Melih Gokcek.
Turkish police detained six people over the killing, state media said on Tuesday. The state-run Anadolu agency said the attacker's mother, father, sister and two other relatives were held in the western province of Aydin, while his flatmate in Ankara was also detained.
After the initial shot, the attacker approached Karlov as he lay on the ground and shot him at least one more time at close range, according to an AP photographer at the scene.
He paced angrily around the body, while shouting, and also smashed several of the framed photos on exhibition, but later allowed the stunned guests to leave the venue.
The spectacle of Karlov's assassination by a member of the Turkish security forces, at a photography exhibition meant to highlight Russian culture, reinforced the sense of unease over the region's conflict and complex web of alliances and relationships.
|The gunman referred to the situation in Aleppo after he shot the ambassador [Burhan Ozbilici/AP]
Several media outlets reported a gunfight later ensued after Karlov was shot.
Local broadcaster NTV television said at least three people were wounded and were taken to the hospital.
Mayor Gokcek told reporters outside the exhibition centre that the "heinous" attack was aimed at disrupting newly re-established relations between Turkey and Russia.
Presidents Vladimir Putin and Recep Tayyip Erdogan spoke by phone about Monday's attack.
"On behalf of my country and my people I once again extend my condolences to Russian President Vladimir Putin and the friendly Russian people," said Erdogan.
The implications of Andrey Karlov assassination
Putin promised a response to the assassination.
"The crime that has been committed is undoubtedly a provocation aimed at derailing the ties between Russia and Turkey, as well as the peace process in Syria," said Putin from Moscow. "There is only one possible response to this - the strengthening of the fight against terror, and the bandits will feel it themselves."
Relations between Russia and Turkey were badly strained by the downing of a Russian warplane at the Syrian border in November 2015, but Turkey's apology earlier this year helped overcome the rift.
Russia and Turkey have co-sponsored the evacuation of civilians and rebels from Aleppo and discussed the prospect of organising a new round of peace talks in Kazakhstan's capital, Astana.
'Don't forget Aleppo'
The assailant referred to the situation in Aleppo after he shot the ambassador in the back.
"Don't forget Aleppo, don't forget Syria," the attacker said in Turkish, after gunning down the ambassador, as seen in a video shared by Turkish media from the scene.
"Whoever took part in this cruelty will pay the price, one by one ... Only death will take me from here," the man said while holding a pistol.
He then continued in Arabic, saying: "We are the descendants of those who supported the Prophet Muhammad, for jihad."
Diego Cupolo, a photojournalist in Ankara, told Al Jazeera there were about 100 armed soldiers in camouflage and police officers at the scene, along with armoured fighting vehicles.
The attack came a day before a meeting of Russian, Turkish and Iranian foreign and defence ministers in Moscow to discuss Syria.
Ankara focuses on Gulen links in Karlov assassination
Those talks will go ahead on Tuesday despite the murder of Karlov, the Interfax news agency said, citing Leonid Slutsky, a senior parliamentarian.
The Russian ambassador to Turkey was a career diplomat.
Karlov joined the diplomatic service in 1976. He served as Russia's ambassador to Pyongyang in 2001-2006, and later worked as the chief of the foreign ministry's consular department.
He had served as the ambassador to Turkey since 2013.
|The assailant is seen in this photo at the rear on the left [Burhan Ozbilici/AP]
Source: Al Jazeera and news agencies